1. Field of the Invention
This invention relates generally to a laser-based navigation system, and a method for using the same, that can absolutely locate, in two dimensions, a reference axis of a mobile vehicle within a given structured environment and more particularly, to a mobile, compact and inexpensive laser-based system utilizing a single low-power laser beam for locating a mobile vehicle in terms of two coordinates related to a structured environment.
2. History of the Prior Art
Robot vehicles have found broad acceptance in a variety of fields, e.g., for transporting raw materials, components and finished products in manufacturing facilities, mining equipment, and special purpose vehicles adapted for particularly hazardous situations. In a dramatic example, the nuclear power plant accident at the Chernobyl facility in the U.S.S.R. in 1986 required the use of robot vehicles to carry exploratory test equipment in zones of lethal radiation. As robots find wider acceptance among the public at large, it may reasonably be expected, therefore, that the need for compact and effective robot navigation systems will become significant.
Where robot vehicles generally track the same path repeatedly, e.g., in a factory environment where there is stationary equipment and machinery to be avoided, guidance pathways often are established within or on the tracked floor and sensors mounted on the vehicle are utilized to guide the vehicle along specific pathways. Such systems, however, are relatively inflexible. Also, even if the vehicle moves accurately along a preselected path, difficulties frequently arise if the path is blocked or obstructed.
An alternative approach has been to utilize pulse data generated by the rotation of the vehicle wheels or tracks and processing such data to monitor and correct the path selected by the vehicle with reference to established reference points in the environment. Wear and tear on the equipment of slippage of the vehicle wheels and various extraneous inputs can, however, lead to errors in such systems.
U.S. Pat. No. 4,500,970, to Daemmer, discloses a robot vehicle guidance system which employs both relative motion sensors, to establish movement behavior along a preselected guide path, and relative motion programmed devices with apparatus for initially identifying environmental checkpoints and initially establishing the orientation of the vehicle with respect to these checkpoints. The propulsion system for the robot vehicle is responsive to both the relative motion guidance signals (for intermediate navigation between the checkpoints) and to the vehicle-checkpoint alignment information (to realign the vehicle with respect to the checkpoints). The vehicle carries a sensor array, which can be a series of mechanically operated electrical switches, ultrasound range detectors or any other suitable sensor which detects the proximity of a selected checkpoint, e.g., a wall or a corner between two walls. When the distance between the detector and such a checkpoint is such that all detector outputs are valid, the various outputs are utilized to determine the vehicle alignment with respect to the checkpoint. This information enables the vehicle, when it is caused to depart from its preselected path by extraneous factors, to take corrective measures and compensate for any incidental deviations in its motion.
An alternative approach is disclosed in U.S. Pat. No. 4,119,900, to Kremnitz, as particularly suitable for the automatic orientation and control of a robot operating on a surface, e.g., an area to be vacuum cleaned or a lawn to be mowed. This device employs a plurality of distance-measuring devices, which continuously and repeatedly measure distances from the robot to points or small surface areas defining the surface to be worked. Electro-optical distance measuring devices are utilized in the far range, electro-acoustical devices are utilized in the close range, and electro and/or mechanical means are utilized within contact range. The various distance measuring device continuously ascertain values of distance, which are then provided to a data processor which transforms the same into digital control signals for the drive means and for tools carried by the robot. The robot thus plans its own driving and working strategies as the result of changing distance measurements.
Both the Daemmer and Kremnitz systems are relatively complex. For many applications it is necessary and, in fact, sufficient to know the exact location of the navigation system and the vehicle on which it is mounted within a two-dimensional framework related to a structured environment, e.g., a large substantially flat area over which the vehicle travels. A need therefore exists for a small, compact, low-cost navigation system that can operate relatively independently of extraneous influences in two-dimensions.